Greece's president has summoned leaders of the country's fractious political parties to a Sunday meeting in a last-ditch effort to form a new coalition government.

Greek President Karolos Papoulias said Saturday he would meet with conservative leader Antonis Samaras, radical left chief Alexis Tsipras and socialist leader Evangelos Venizelos after all three failed to gather enough support to create a new government. Mr. Papoulias' office also said he would meet separately with the leaders of four other parties that won enough votes in last Sunday's splintered election to gain seats in parliament.

None of the country's political parties came close to winning enough seats to form a government on its own. Now, Mr. Papoulias has until next Thursday to broker a deal to create a coalition government. If he fails, Greece will have to hold new elections in June.

The key point of contention centers on the debt-ridden Greek government's acquiescence to the demands of its international lenders and European neighbors to impose sharp austerity measures in exchange for approval of its second bailout in two years.

Samaras and Venizelos supported the social spending cuts, but Tsipras says voters repudiated the austerity agreement and that Greece is not obligated to carry it out. Greeks have frequently taken to the streets in massive, sometimes violent protests against the plan calling for higher taxes, reduced pensions and elimination of thousands of government jobs.

But European leaders have warned the Athens government that it must carry out the austerity measures or they will not send it more bailout money. Financial analysts say that Greece could default on its financial obligations and become the first country to leave the 17-nation euro currency union.

On Friday, Venizelos announced that the Radical Left Coalition, or Syriza, refused to join the Socialists and conservatives in a unity government. The Socialist and conservative New Democracy parties have proposed a gradual phasing out of the tough measures imposed by the European Union and International Monetary Fund. The leftists want those measures canceled immediately.

Greek voters punished both the Socialists (PASOK) headed by Venizelos and New Democracy led by Samaras for having pushed through the tough economic austerity measures. The two parties have traditionally won 80 percent of the votes in Greek elections, but last Sunday only collected 32 percent.

New Democracy won the most parliamentary seats in the voting, followed by the Radical Left and the Socialists. New polls show the Radical Left gaining strength since the voting a week ago.